On 19.4.2021 22.05, Ole Salscheider wrote: > Hi Mathias, ... >> tracing shows the content of the TRB while it's written, before writing the cycle bit. >> Could be worth dumping transfer ring after issue is seen and check TRB still looks valid: >> cat /sys/kernel/debug/usb/xhci/<your controller>/devices/<xx>/ep<yy>/trbs >> you need to figure out which controller, device and endpoint number for this. > > I think this is the output for the correct device and endpoint: > > https://stuff.salscheider.org/trbs Thanks, the TRB was already turned No-op by the cancel code by then, but it doesn't matter, your trace below indicates the TRB is fine. > >> How about your delayed link TRB cycle write patch? did it help trigger an event for the last transfer >> TRB, or did it just help as controller couldn't go past the link TRB and was less out of sync with >> the driver? > > > You can find a trace of recording a few seconds of video with my patch here: > > https://stuff.salscheider.org/trace_with_patch > > As far as I can tell from it, the patch helps to trigger an event for all transfer TRBs. I also tried to record around 30 min of video with it and it did not encounter a problem while recording. > > I however cannot start a new recording after stopping the first. And sometimes I observe hangs of the computer some time after stopping the recording. That might be some unwanted side-effect of my patch... > Yes, It shows transfer events for the TRBs before the link TRB. This workaround is however a can of worms as many TD's consist of several TRBs, and they only trigger events for the last TRB. How about a different approach? If the issue is only with transfers starting on the last TRB before the link TRB, we could turn that TRB to a no-op. Does something like the code below help? diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index 6cdea0d00d19..0ffda8127640 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -3181,6 +3181,12 @@ static int prepare_ring(struct xhci_hcd *xhci, struct xhci_ring *ep_ring, } } + if (ep_ring != xhci->cmd_ring && + !trb_is_link(ep_ring->enqueue) && + trb_is_link(ep_ring->enqueue + 1)) + queue_trb(xhci, ep_ring, 0, 0, 0, 0, + TRB_TYPE(TRB_TR_NOOP) | ep_ring->cycle_state); + while (trb_is_link(ep_ring->enqueue)) { /* If we're not dealing with 0.95 hardware or isoc rings * on AMD 0.96 host, clear the chain bit. -Mathias
